Conventionally, in order to impart novel properties, in addition to the original properties of rubber, to rubber products, filler and the like of various materials or shapes are introduced into rubber compositions according to the uses to achieve the desired properties. For automobile tires, for example, in order to improve properties such as abrasion resistance, low-heat-build-up properties, or wet grip performance, filler (e.g., silica, carbon black) is introduced into the organic rubber fraction.
When filler or the like is mixed with the rubber fraction in such a rubber composition, for the purpose of enhancing the affinity between the two to improve low-heat-build-up properties, wet grip performance, etc., a modified rubber (modified diene polymer) has been used in which a functional group having affinity for the filler is introduced in rubber molecules in the rubber fraction as a result of, for example, a treatment involving reacting rubber molecules with, for example, a compound containing both a nitrogen atom-containing group and a chlorosulfenyl group (see, for example, Patent Literatures 1 and 2).
It is however known that, depending on methods for introduction, a predetermined functional group is difficult to introduce to a predetermined position in the rubber molecule and is consequently introduced to, particularly, a random position in the main chain constituting the rubber molecule. Use of such rubber molecules containing a predetermined functional group introduced in the main chain is less likely to produce the desired effects due to the random bonds between the rubber molecules and filler. In addition, the functional group-introduced sites have deteriorated rubber properties, which disadvantageously results in deterioration in the properties of the whole rubber.